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Calculate surface air consumption (SAC) rate for scuba divers. Enter tank PSI used, dive time, and depth to estimate cu ft/min at the surface.
Plan safe recreational scuba dive profiles from air supply, depth, and SAC rate. Estimate bottom time, turn pressure, and remaining gas at ascent.
Calculate proper scuba diving ballast weight for neutral buoyancy. Estimate lead needed from body weight, exposure suit, tank type, and water salinity.
Convert depth to atmospheres of water pressure and add 1 ATA for surface ambient pressure. At 66 ft, absolute pressure is 3 ATA — you consume gas three times faster than at the surface.
P_abs = 1 + (Depth ft ÷ 33)Multiply personal surface air consumption by absolute pressure to get actual volumetric consumption rate at the planned depth.
Rate (cu ft/min) = SAC × P_absConvert cubic feet per minute back to tank pressure drop per minute using tank rated volume and working pressure. This is what you observe on your SPG during the dive.
PSI/min = (Rate × Max PSI) ÷ Tank size (cu ft)Updated: July 2026
At 90 ft with SAC of 0.85 cu ft/min, expect roughly 75 PSI/min drop on an aluminum 80. A 1000 PSI drop occurs in about 13 minutes — plan turn pressure accordingly.
Increased exertion raises SAC from 0.7 to 1.1 cu ft/min. Recalculate consumption at depth before committing to a long swim against current.
Minimal movement often yields lower SAC. Track consumption over several dives to establish a baseline for macro photography sessions at 40–50 ft.
Air consumption increases linearly with absolute pressure at depth. Enter your SAC rate, target depth, and tank parameters to calculate actual breathing rate underwater, PSI consumed per minute, and estimated time until reaching reserve pressure.